Cold sintering of yttria-stabilized cubic bismuth oxide: Conductivity and microstructural evolution of metastable grain boundaries with annealing

Yttrium-doped bismuth oxide (BYO) is densified by the cold sintering process (CSP) at 300 °C. The relative density reached is ∼90% of the theoretical density. The as-sintered BYO ceramic shows a total conductivity of >1 mS/cm at 500 °C. The conductivity slightly increased after the annealing process. The scanning and transmission electron microscopy analysis revealed that a metastable secondary phase formed adjacent to BYO grains in the as-CSP specimens. Once annealed, the secondary phase recrystallized and there is an associated total conductivity improvement.